The invention relates to forming thermally curable materials on a support structure in an electronic device.
Electronic packaging (including packaging of one or more dies into an integrated circuit housing; packaging chips into multichip modules; and attaching chips onto a printed wiring board or PWB) involves forming thermally curable materials on the underlying support structure (which can be a wafer, PWB, leadframe, or other support surface). After formation of the thermally curable material, such as by screen printing, the material is cured to properly bond the material to the surface of the support structure.
For example, to attach chips to a PWB or other support surface, solder or a conductive adhesive can be deposited onto the support surface through a screen in a screen printing machine. After the solder or conductive adhesive has been formed, the support surface is removed from the screen printing machine and placed in an oven to cure the solder or conductive adhesive at high temperatures.
Another process that involves formation of a thermally curable material onto a support surface is flip-chip bonding, in which an unpackaged die is mounted directly onto a support structure (also referred to as an interconnecting substrate). The unpackaged die is turned upside down and bonded to the interconnecting substrate by some connecting medium, including solder bumps and conductive adhesives that contains polymers such as metal-filled epoxies or conductive thermoplastic compounds.
Flip-chip bonds provide a high density, low inductance direct electrical path between the die and the interconnecting substrate. Referring to FIG. 1, a typical flip-chip assembly is shown. An interconnecting substrate 10 has a surface 18 that provides conductive terminals 12. To prevent bonding material from flowing in the region between conductive terminals 12, solder dams 14 are mounted on the interconnecting substrate 10 between adjacent terminals 12.
A die 16 for mounting to the interconnecting substrate 10 is flipped over so that its active surface 21 faces the top surface 18 of the interconnecting substrate. Bumps 20 (solder or adhesives) are formed on bond pads 22 (typically made of aluminum) on the surface 21 of the die 16. As shown by the enlarged cross-sectional portion of the die 16, a window is cut through a passivation layer 24 over each bond pad 22 so electrical contact can be made. One or more thin circular layers 26 are formed over the exposed surface of the bond pad 22. Next, solder bumps or conductive polymer bumps 20 are formed over the circular layers 26, using such dispensing techniques as screen printing or pneumatic dispensing.
Typically, the formation of the layers 26 and bumps 20 is performed on an entire wafer, which includes multiple dies. After the layers 26 and bumps 20 are formed, one or more wafers are placed inside an oven to enable the bumps 20 to bond to the layers 26. Solder bump connections are made using a reflow process, which takes the plated solder through a solid-liquid-solid transition, allowing the solder to bond with the layers 26. If thermoset conductive polymers such as metal-filled epoxy are used, then the oven heating cures the thermoset polymer so bonding can occur.
Next, the wafer is sawed into individual dies. Each die 16 is placed onto the interconnecting substrate 10 such that the bumps 20 contact corresponding conductive terminals 12 on the interconnecting substrate 10.
In the typical manufacturing processes described above, support surfaces (wafers, PWBs, etc.) are physically removed from a screen printing or pneumatic dispensing machine and loaded into an oven to cure the deposited thermally curable material, which can be labor-intensive and time-consuming.
Generally, the invention is directed to formation of a thermally curable material on an electronic device support structure that is placed on a heatable surface. Curing of the thermally curable material can then be performed by heating the heatable surface.
The invention has one or more of the following advantages. Using an in-line process to form thermally curable material on a support structure followed by thermally curing the material, steps in the manufacturing process are reduced. By eliminating the need to physically move support structures from one system to another system, first to deposit a thermally curable material and subsequently to cure the material, time and labor can be saved.
In general, in one aspect, the invention features a method of forming a thermally curable material on a support structure in an electronic device. The method includes placing the support structure on a heatable surface, and depositing the thermally curable material onto a surface of the support structure. The heatable surface is then heated to a temperature sufficient to cure the deposited material.
In general, in another aspect, the invention features a method of forming bumps on bond pads on a die. The die is placed on a heatable surface. Thermally curable bumps are formed on the bond pads. The heatable surface is heated to a temperature sufficient to cure the bumps.
In general, in another aspect, the invention features a method of fabricating a flip-chip assembly. A thermally curable material is deposited onto bond pads on a die placed on a heatable surface. The heatable surface is then heated to a sufficient temperature to cure the thermally curable material. The die is face mounted onto an interconnecting structure by connecting the cured material on the die bond pads to corresponding terminals on the interconnecting structure.
In general, in another aspect, the invention features a method of forming structures on a semiconductor die. A thermally curable material is screen printed onto bond pads of the die using a screen printing machine. The thermally curable material is heated in the screen printing machine to a temperature sufficient to cure the material.
In general, in another aspect, the invention features a screen-printing system including a member for holding an electronic device support structure, the member capable of being heated. The screen printing system further includes a screen through which a thermally curable material can be deposited onto portions of the support structure. The heated member is adapted to cure the material after deposition of the thermally curable material onto the support structure.
In general, in another aspect, the invention features an apparatus for forming a predetermined pattern on an electronic device support structure using a thermally curable material. A device is configured to deposit the material onto the support structure. A heatable surface on which the support structure is positioned is heated to a temperature sufficient to cure the material.
Other features and advantages will become apparent from the following description and from the claims.